1. Field of the Invention
The present invention relates to a developing apparatus used in an image forming apparatus such as a copier, a facsimile machine, a printer, a multi-function, and more particularly to a developing apparatus for developing a latent image on a latent image carrier by applying developer thereto.
2. Description of the Related Art
As a known image forming apparatus, there is, for example, a tandem type image forming apparatus which forms color images by superposing plural toner images of various colors with plural corresponding toner image forming parts (including, for example, a photoconductor and a developing apparatus) arranged in a horizontal direction. In the tandem type image forming apparatus, it is desired to reduce the interval between the plural toner image forming parts for achieving size-reduction of the image forming apparatus. Accordingly, in a known developing apparatus, a large space developer storing chamber for storing developer therein is provided above a developer supplying chamber having a roller for supplying the developer to a developing roller. This reduces the size in the horizontal direction of developing apparatus.
In one of the developing apparatuses having a developing roller and a supplying roller below the developer storing chamber, a partitioning member having a developer supplying port is provided between its developer storing chamber and the developer supplying chamber. Although this developing apparatus can supply developer from its developer storing chamber to its developer supplying chamber by gravity, the developer may be excessively supplied to the developer supplying chamber. In this case, the increase of pressure applied to the vicinity of the developing roller and the supplying roller by the weight of the developer may cause overfilling of developer in the developer supplying chamber. This causes the rotational torque of the developing roller and the supplying roller to increase and results in problems such as uneven image density or damage of gears due to uneven rotation of the developing roller and the supplying roller in the developing apparatus. Furthermore, the overfilling also adversely affects the flow in the developing apparatus. Accordingly, developer cannot be evenly supplied to the surface of the developing roller and results in poor image density due to an uneven layer of developer formed on the developing roller. Furthermore, in a case of using a developer with wax added for conducting oil-less fixation or low temperature fixation, the soft characteristic and the high aggregating property of the developer tend to promote the aforementioned problems.
In Japanese Laid-Open Patent Application No. 2001-194883, there is proposed an apparatus for reducing the size of the opening of the partitioning member between the developer supplying chamber and the developer storing chamber so that the developer supplied to the developer supplying chamber can be maintained in a suitable amount and prevent overfilling of developer in the developer supplying chamber. Furthermore, in Japanese Laid-Open Patent Application No. 2001-194883, a wing member is provided at a bottom part of the developer storing chamber for allowing a suitable amount of developer to be supplied from a developer supplying port by the rotation of the wing member. Accordingly, the developer supplied to the developer supplying chamber can be maintained in a suitable amount and this prevents overfilling of developer in the developer supplying chamber. However, since the consumption rate of developer varies, it is difficult to supply a suitable amount to the developer supplying chamber and prevent excessive supply to the developer supplying chamber. Furthermore, once the developer is excessively supplied to the developer supplying chamber, the developer supplying chamber may remain in such an excessively supplied state for a long period of time until the developer is consumed.
Furthermore, in the configuration where the developer supplying chamber and the developer storing chamber are partitioned by the partitioning member, the developer supplied to the developing roller circulates only inside the developer supplying chamber. This accelerates degradation of the developer in the developer supplying chamber and makes it difficult for the developer to maintain a consistent characteristic (e.g., charging property).
Japanese Laid-Open Patent Application No. 6-64398 discloses a developer apparatus having a roller provided in a connecting port between a developer storing chamber and a developer supplying chamber and plural flexible flaps (wings) arranged at the periphery of the roller. With this developing apparatus, developer is supplied from the developer storing chamber to the developer supplying chamber and also the developer is transported back to the developer storing chamber from the developer supplying chamber. By transporting the excessively supplied developer from the developer supplying chamber back to the developer storing chamber, the overfilling of developer in the developer supplying chamber can be prevented. Furthermore, since the developer can circulate between the developer supplying chamber and the developer storing chamber, the degradation of developer in the developer supplying chamber can be prevented. However, the roller provided at the connecting port between the developer supplying chamber and the developer storing chamber and the flexible flaps have a complicated shape and require to be precisely positioned for supplying/transporting the developer. Furthermore, with the developing apparatus, it is difficult to attain endurance and maintain consistency with time.
From another aspect, as one type of developing apparatus, there is a developing apparatus that develops a latent image on a latent image carrier by using a developer carrier that carries developer supplied from a developer supplying member. In this type of developing apparatus, the developer carrier and the developer supplying member (supplying roller) for supplying developer to the developer carrier are provided inside a developer storing chamber of the developing apparatus. In this developing apparatus, the developer storing chamber is long in a horizontal direction according to a cross-sectional view in the axial direction and has a conveying member for conveying the developer inside the developer storing chamber in the horizontal direction for supplying a suitable amount of developer to the supplying roller.
Meanwhile, in recent years and continuing, a tandem type image forming method is used by color image forming apparatuses for achieving high speed printing. As described above, in the tandem type image forming method, plural sets of latent image carriers (e.g., photoconductors) and developing apparatuses for developing the latent images on the latent image carriers are successively aligned for superposing images of different colors and transferring the superposed images onto an intermediary transfer belt or a sheet of paper. Thereby, a color image (e.g., full color image) can be formed. However, since such an image forming apparatus has plural sets of latent image carriers and developing apparatuses aligned in a horizontal direction where each developing apparatus has a developer storing chamber which is long in the horizontal direction, the image forming apparatus requires a large amount of space in the horizontal direction, thereby resulting in an image forming apparatus which is oversized in the horizontal direction.
As another type of developing apparatus, there is a developing apparatus having a developer storing chamber which is longer than it is wide. This developing apparatus supplies developer to the supplying roller by utilizing the weight of the developer in the developer storing chamber situated above the supplying roller. This configuration reduces the space in the horizontal direction. However, with this configuration, the developer falling onto and accumulating on the supplying roller leads to problems such as increase of torque of the supplying roller and wear of the supplying roller. Furthermore, the toner on the supplying roller may aggregate and lead to uneven image density. These problems may easily occur in a case where wax is contained in the particles of the toner for achieving oil-less fixation or low temperature fixation. Since this type of toner is relatively soft and has particles with a relatively high adhering property, the toner easily aggregates on the supplying roller.
In the aforementioned Japanese Laid-Open Patent Application No. 2001-194883, the developing apparatus has a first storing chamber including a developer carrier and a supplying roller, a second storing chamber for containing a large amount of toner, and a partitioning wall having plural supplying ports. The partitioning wall serves to reduce the pressure applied to the supplying roller by the weight of the developer and prevent problems such as increase of torque of the supplying roller and wear of the supplying roller. Furthermore, the plural supplying ports provided in the partitioning wall allow a suitable amount of toner to fall onto the supplying roller.
However, with the developing apparatus of Japanese Laid-Open Patent Application No. 2001-194883, there is a difference in the amount of developer conveyed from the area facing the supplying port and the amount of toner conveyed from the areas other than the area facing the supplying port. Therefore, the developer cannot be evenly applied to the surface of the supplying roller in the axial direction.
Accordingly, in order to evenly apply toner to the surface of the supplying roller in the axial direction, a conveying member may be provided between the supplying roller and the supplying port for conveying the toner in the axial direction. Furthermore, by providing the conveying member, the toner in the first storing chamber can be agitated, to thereby prevent toner from aggregating.
However, since the toner in the area directly below the supplying port is conveyed in the axial direction, a space (gap) is created in the first storing chamber at the area directly below the supplying port. In order to fill this space, developer from the second storing chamber is supplied (supplemented) to the space via the supplying port. As a result, toner is excessively supplied to the first storing chamber and overfills the first storing chamber. This results in problems such as aggregation of toner, increase of torque of the supplying roller, and uneven image density.
Furthermore, as another conventional developing apparatus, Japanese Laid-Open Patent Application No. 1-292375 discloses a developing apparatus having a developer supplying port provided at a bottom part of a developer storing container above a developer supplying chamber. However, in this developing apparatus as well as the above-described conventional developing apparatuses, except for the vicinity of an opening formed in a partitioning member between the developer storing chamber and the developer supplying chamber, toner tends to remain (accumulate) at a partitioning member. Thus, toner cannot be efficiently used to the end.